Nutrient Digestion and Digestibility Flashcards
what is nutrient digestibility
- chemical analysis of feed provides information on nutrient composition
- no information on digestibility in digestive tract (extent of digestion important
- indication of bioavailability of nutrients (nutrients that is available for metabolism)
what is digestibility
- the proportion of a feed that is not excreted in the feces and, therefore is assumed to have been absorbed
- major determinant of nutritional value of feeds
digestible matter + undigestible matter = 100%
what is the concept of digestibility
high digestibility = high nutritional retention = high performance (positive for economics, less so for environment (manuer = nitrogen and phosphorus)
low digestibility = low nutrient rentention = poor performance
what are the methods of measure for feed digestibility
- in vivo
- in sotu
- in vitro
what is in vivo
- total fecal collection
- indicator method
what is in situ
- nylon bag
what is in vitro
- tilley and terry method
- gas prodcution
- enzymes
- regression using chemical analysis
what are step in vivo measurement of digestibility
- test feed or diet given to animal in known amounts for several days - 4-14 adaption period (4-7 days to measure feed intake then collect feces)
- 4-6 animals fed test or diet, digestibility differs; statistical analysis requires replication (consistent feed intake; time of feeding)
- can use males of females
- housed in metabolism crates or stalls, measure fecal output
why do you need an adaption period for feed
- allow time for old feed to be totally excreted (so only test feed is in the diet)
- might take animals GI a bit of time to adapt to the new feed - microorganisms
- feed intake might go down = environmental adaptation to new feed
what are metabolism crates
- sheep and pigs- adaptation periods
- fecal collection - fecal bags or tray behind animal
- urine - delivered by funnel into collection Jar below
how do you use digestibility for total fecal collection
- determine DM % and nutrient content of test feed ( CP crude fat NDF ADF)
- feed animal in metabolic crate, measure FI
- collect total fecal output
- determine DM % and nutrient content in feces
- determine total DW or nutrient intake and total DM or nutrient output in feces
what is the difference between apparent and true digestibility
- most measurements of digestibility are apparent nutrient digestibility
- enzymes + sloughed-off epithelial cells + microbial cells in feces = endogenous losses
- when we dont account for endogenous loss = apparent
- when we do account for endogenous loss = true protein ( true should always be higher, because in apparent you over estimate protein)
what are indirect measurement of digestibility
- some feed ingredients cannot be fed as sole feed ( 100% grain to a ruminant (rumen acidosis) or 100% fat to any animal)
- measure digestibility indirectly using two digestibility trials
- first, determine digestibility of a basal diet which can be fed at the 100% level (the only feed the animal is getting)
- then combine the basal with the test ingredient and measure the digestibility of the basal diet and the test ingredient in combination
what is step 1 in indirect measurement of digestibility
- determine digestibility of the basal diet
- 60% digestibility of alfalfa
what is step 2 in indirect measurement of digestibility
- determine the digestibility of 50/50 alfalfa/grain (5kg each on DM basis)
- fecal output = 2.5 kg
- partition the feces source
- 5 kg of alfala = 2 kg of feces (calculation)
- 10kg of feed = 2.5 feces by test
- 5 kg of grain = 0.5 kg feces by difference
- ## digestibility of grain
what are problems with total collection
- need accurate estimate of feed intake (feed wastage, animals on pasture)
- must collect all fecal output ( volume of material can be large =, tedious and labour-intesive)
how do you measure digestibility with indicator method
- mix an indigestible indicator into the feed at a low and known level (usually 0.5%) (with adataptation period
- feed to an animal (no need to measure intake)
- collect a grab sample of feces (no need to collect all)
- measure concentration of indicator in feces
what are the properties of ideal indicator or marker
- cannot be digested or absorbed from GI
- inert, no toxic metals or metabolic effects
- intimately associated with material that it is to mark (the diet )
- uniformly excreted in feces (grab samples)
- stable
- inexpensive
- readily available
- easily detected, easy to measure
what is an example of an internal digestibility marker
- indigestible NDF
- lignin (good for browse)
- acid insoluble ash ( silicates)
what is an example of an external marker of digestibility
- chromic oxide (Cr2O3) - chemically added
- titanium oxide or ytterbium - more expensive/ more difficult
what is an in vitro techniques and in situ technique for watching digestibiltiy
- stimulate rumen fermentation and small intestinal (gastric digestion) under controlled conditions
- test tube
what is tilley and terry
artificial rumen
what is a nylon bag
have the feed placed in a nylon bag and place it in the GI
- 5cm x 15cm 50um filled with 2-5g ground feed sample
- pore size is important ( test feed in bag and tie tighly
- slowly digestible
- incubate in rumen for predetermined lengths of time 0-48 hours
0 accounts for original feed, making sure none is lost
wash bags, dry measure residue weight) CP NDF ADF
what is the tilley and terry method
- rumen fluid obtained from fistulated animals to provide source of rumen micro-organisms
- digest feed (0.5g) with rumen liquor (same as rumen fluid) in system where CO2 is bubbled into tube to maintain anaerobic conditions for 48h at 39c
- buffers so ph incubation doesnt go down to much
- a second digestion is conducted using pepsin (50ml of 0.2% solution) for further 48h 39c
- the undigested residue is weighed and nutrient digestibility estimated
- incubate blank with ruminal fluid + buffer (not adding a feed to the blank flask, can get feed out of rumen)
- can process large number of samples, quickly (rumen fluid is divided into many test tubes)
- yields comparable data to in vivo
- diet of donor animal, inoculum processing, length of incubation, sample processing ect. can insluence results
- must grind original sample
- must be consistent
what is mobile nylon bag technique
- nylon bag technique useful for determining feed digestibility in ruminant
what issue happened with swine researchers
- the fed bags were chewed and let feed escape
- inserted bags into stomach, but got trapped in stomach bags could not pass plyloric sphincter
what happened swine researchers positively
- mimic digestion in the stomach by incubating bags with pepsin and Hal; then insert bags into the duodenum
- you have to sit there and wait for feces, collect and look for bags to avoid continous microbial breakdown and put it in water
what feed factors affect digestibility
- level of dietary fibre
- composition of fibre (when fibre goes up digestibility goes down)
- stage of maturity of plant
- processing of feed
- anti-nutritional factors
- feed additives
how does fibre effect digestibility
- as plants mature - the fibre content goes up
- digestibility of the plant goes down
- (less enzyme penetration of the cell wall - especially is lignin is high)
what are the effects of composition of fibre on digestibility
- fibre = cell wall content = cellulose + hemicellulose + lignin
- cellulose and hemicellulose can be partially digested
- lignin is indigestible
- fibre with high lignin content is less digestible
what are the effects of processing on digestibility
- grinding and devilling
- improves feed digestibility (particle zise reduction, removes barrier to enzyme penetraction
- processing effects greater with pooer quality feeds (grinding has greastest inpact with high fibre feeds)
effects of grinding in ruminants
- can improve digestibility
- excessive grinding of forages can be detrimental (reduces salvia secretion, reduces rumination and decreases the ratio of acetate to propionate)
- greater rates of passage through rumen can reduce digestibility
effects of anti-nutritional factors on digestibility
- some feeds can contain anti-nutritional factors
(trypsin inhibator - raw soybeans, tannins faba beans, glucosinolates (rapeseed) - can significantly reduce nutrient digestibility
effects of feed additives on digestibility
- use of exogenous enzymes to improve the nutrition value of feeds (major focus of research)
- phytases, B glucanases and xylanases
what is phytate
- 60-75% of p in cereal grains bound as phytate
- phytate utilization in monogastric low (no phytase expression)
- dietary inclusion of inorganic P to meet the animals requirement
- also P excretion
what is phytase
- improves P digestibility in cereal grains
- benefits ( can reduce inorganic P) ( reduce feeding costs; environment benefit )
what is the enviropig
- genetically - engineered pig
- can use phytate P
- No P supplementation - 65% less manure P; save on feeding costs
what are animal factors that can affect digestibility
- species of animal
- age of animal
- level of feeding
- health status
effect of animal species on digestibility
- digestibility coefficients for feeds variable (type of animal fed, conditions under which the feed is fed)
- ruminants vs non ruminants (fibre digestibility
effect of age of animal on digestibility
- the ability to digest fibre sources increases with age (develops with rumen)
- larger fore-stomachs or hind-gut
- ## expression of digestive enzymes also increases
effects of level of intake on digestibility
- at high levels of intake, rate of passage increases (reduces digestibility)
- fibre digestion in ruminants
- faster rate of passage reduces digestibility = less opportunity to digest
- reduces ability of fermentation
how does cold temperature effect digestibility
- cold temperature reduces digestibility because of the higher increase of DM eaten
how do seasons effect nutrient digestibility
- greater water consumption in the summer increases passage rate
- making intake go up and decreases digestibility
- consuming more water, because of water lost due to panting and sweating
